1.

Explain entropy changes for various phase changes.

Answer»

SOLUTION :A phase CHANGE always takes place at CONSTANT pressure and temperature. During a phase change, both the phases exist at equilibrium.
(1) Entropy change for fusion of a solid :
`underset("(ice)")(H_(2)O_(s)) overset(Delta_("fus")H^(0))tounderset("(water)")(H_(2)O_((l))) OR " Solid" overset(Delta_(fus)H^(0))to"liquids"`
If `Delta_("fus")H^(0)` is the standardenthalphyof fusion atabsolutetemperatureT,then theentropychangewill be ,
`Delta_("fus")S = (Delta_(fus)H^(0))/(T)`
(2) Entropy change for varporisationof a liquids.
`underset("(water)")(H_(2)O_((l))) overset(1 atm, 100^(@)C) to underset("(vapour)")(H_(2)O_((g)))` OR `"Liquid" to "vapour"`
If `Delta_(vap)H^(0)` is the standard enthalphychangefor evaporationat absolute temperatureT, thentheentropychangewill be .
`Delta_(vap)S = (Delta_(vap)H^(0))/(T)`
(3) Entropy changefor the sublimationof a solid .
`"Solid" tooverset(Delta_("SUB")H^(0))"Vapour"`
If `Delta_("sub")H^(0)` is the standard enthalphychange for thesublimationat absolutetemperatureT then,theentropy changewill be .
`Delta_("sub")S = (Delta_("sub"H^(0)))/(T)`


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